This invention relates to a denture-base made of a compound comprising thermoplastic resins having different properties, which is excellent in appearance, mechanical properties, repairability etc.
Denture-bases have been produced for many years from acrylic resins by compression molding method wherein their polymers and monomers are polymerized by heat. An advantage of the acrylic resin denture-bases is that they can be readily repaired by use of acrylic polymer powders and acrylic monomer liquid as repair materials.
The acrylic resin denture-bases thus produced by thermal polymerization are, however, weak in strength so that thin portions therof are often broken by occlusal forces. In addition, the said denture-bases might be poisonous so as to cause allergy due to effluence of residual monomers resulting from incompletion in thermal polymerization reaction.
Denture-bases made of thermoplastic resins such as polysulfone have also been proposed and practically used to eliminate the above drawbacks of acrylic resins, which are produced by injection or compression molding in gypsum molds.
The denture-bases of thermoplastic resins such as polysulfone are superior in strength to those made of acrylic resins, because the thermoplastic resins such as polysulfone are excellent in impact resistance compared with conventional acrylic resins. However, the said denture-bases are difficult to repair and cannot endure a long-term use because they tend to have stress-cracking in contact with instantaneous polymerizing resins composed of acrylic monomers, particularly methyl methacrylate which is most commonly used for repairing acrylic resin denture-bases.
The application to denture-bases of polyester or polycarbonate resins such as polycarbonates, polyester carbonates, aromatic polyester copolymers and their mixtures, is under investigation. These resins are superior in compatibility with methyl methacrylate and have few stress-cracking in contact with methyl methacrylate, compared with the polysulfone resins as mentioned above. These resins, however, tend to have stress-cracking in contact with isobutyl methacrylate or normalbutyl methacrylate which is a component of relining resins or repair materials.